EURADOS Report 2026-01 published: "EURADOS ICIDOSE#2 InterComparison of Internal DOSE assessment #2 - Analysing the intercomparison results"

EURADOS Report 2026-01 is published: "EURADOS ICIDOSE#2 InterComparison of Internal DOSE assessment #2 - Analysing the intercomparison results"

T. Pázmándi, D. Bingham, B. Breustedt, D. Broggio, C. M. Castellani, G. Drouet, P. Fojtík, A. Giussani, S. Löscher, J. Osko, A. Pántya, Z. Rékasi, V. Rovenská, D. Spencer

Abstract: Internal dose assessment often requires complex processes and expert judgements. Estimating occupational intakes of radionuclides and the associated committed effective doses require the collection, processing and interpretation of relevant measurement data. This process often involves complex procedures and judgements, such as the selection and application of appropriate biokinetic models and parameters; the identification of appropriate measurement data and evaluation of the uncertainties within those data, as well as the use of default assumptions and the extent of which the assessment should be adapted to case-specific circumstances. Consequently, considerable subjectivity may arise in the assessment process, such that the same data set can lead to substantially different estimates of intake and dose when evaluated by different assessors (IAEA, 1999), (IAEA, 2007). Intercomparisons in internal dosimetry are an invaluable tool for verifying the performance of internal dosimetry services, promoting harmonisation of dose assessments and identifying areas for improvement.
The system for radiation protection is constantly evolving. In recent years new recommendations have emerged in the field of the determination of internal radiation exposure at the workplace. The 2007 Recommendations of the International Commission on Radiological Protection (ICRP, 2007) introduced changes that affect the calculation of effective dose and implied a revision of the dose coefficients for internal exposure. The Occupational Intakes of Radionuclides (OIR) series was published and replaced the previous publications. OIR Part 1 (ICRP, 2015) describes the assessment of internal occupational exposure to radionuclides, biokinetic and dosimetric models, methods of individual and workplace monitoring, and general aspects of retrospective dose assessment. Part 2, 3, 4 and 5 ( (ICRP, 2016); (ICRP, 2017); (ICRP, 2019); (ICRP, 2022)) of the OIR series provide data on individual elements and their radioisotopes, including information on chemical forms encountered in the workplace; a list of principal radioisotopes and their physical half-lives and decay modes; the parameter values of the reference biokinetic model; and data on monitoring techniques for the radioisotopes encountered most commonly in workplaces. Reviews of data on inhalation, ingestion, and systemic biokinetics are also provided for all the elements.
“Technical Recommendations for Monitoring Individuals for Occupational Intakes of Radionuclides (TECHREC)” has been developed as a tool for internal dosimetrists and have been published in the Radiation Protection document series of the European Commission as document RP188. The aims of these recommendations were to encourage harmonisation, to present a complete account of the principles of individual monitoring and internal dosimetry, and to provide comprehensive guidance and recommendations on best practice. To check the practical applicability of the TECHREC Recommendations for an internal dose intercomparison exercise, titled ICIDOSE 2017, has already been promoted in mid-2017 by the “Internal dosimetry” Working Group (WG7) of EURADOS (Roberts, et al., 2020). In order to disseminate the latest scientific results and to verify the practical applicability of these recommendations, another international intercomparison exercise was organized by the EURADOS Working Group 7. The objective of ICIDOSE#2 is to assess internal doses using the latest recommendations (TECHREC RP188, ICRP OIR Report Series, (ICRP, 2015), (ICRP, 2016), (ICRP, 2017), (ICRP, 2019), (ICRP, 2022)) or the relevant accreditation standards (ISO, 2006), (ISO, 2011). ICIDOSE#2 builds on the success of ICIDOSE 2017.
The ICIDOSE#2 intercomparison exercise comprises five cases, each with different levels of complexity, designed to address a range of scenarios from simple to more challenging ones. This approach is intended to address both common or routine issues and less frequent or exceptional challenges encountered in internal dosimetry. Some cases feature only a limited number of early-phase data, whereas others have more extensive data available over extended periods relying on e.g. prolonged monitoring intervals and annual records. The intercomparison exercise covers different case studies, including dose assessments as part of routine monitoring, subsequent follow-up assessments after obtaining insignificant results, as well as the considerations for new intakes necessitating special monitoring.

• Case 1 focuses on the individual monitoring of a worker involved in source production within a hot cell environment. Due to the potential risk of internal contamination with ¹³⁷Cs, a 365-day monitoring program was implemented to confirm safe working conditions.
• Case 2 covers a scenario when a plumber from the technical staff of the hospital was asked to repair an obstructed toilet evacuation system, which led to flooding in the restroom. The plumber remained in the room until the leakage was resolved. After the effluent was evacuated, radioactive contamination of ¹³¹I was confirmed in the toilets. Following the incident, the worker was decontaminated with showers and urine collection was initiated to assess potential exposure.
• Case 3 concerns routine monitoring that was conducted during maintenance work between fusion runs in a facility to check for the presence of low-level tritiated water (HTO) in the workplace.
• Case 4 is a scenario in which a process operator got a small wound to his finger while wrapping waste in a glovebox. The operator was treated at a medical facility and wound monitoring revealed ²⁴¹Am contamination. Over the next eleven days, the wound was monitored for activity and attempts were made to excise the material at the wound site. Daily urine samples were also collected and analysed for ²³⁹Pu, ²⁴⁰Pu and ²⁴¹Am.
• Case 5 refers to a case when in a laboratory handling ³⁵S isotopes, a female worker of childbearing age, who is regularly monitored by urine analysis every 30 days, was potentially exposed to a release of ³⁵S. To assess potential incorporation, she was immediately asked to provide a 24-hour urine sample. However, it was later confirmed that she was pregnant, with conception assumed to have taken place before the incident. Three additional urine samples were collected after the incident for further analysis. In addition to the estimation of the committed effective dose, the exercise also involved the calculation of the uterus dose to the worker and the expected dose to the offspring.